Calorimetric analysis of powder compression: II. The relationship between energy terms measured with a compression calorimeter and tableting behavior

Evaluation of In-Die Compression Data for a Deeper Understanding of Altered Excipient Properties upon Temperature Rise

The thermodynamic analysis of tablet formation includes the thermal and mechanical analysis during compression. The aim of this study was to evaluate alterations of force-displacement data upon temperature rise as an indicator for changed excipient properties. The tablet press was equipped with a thermally controlled die to imitate the heat evolution from tableting on an industrial scale. Six predominantly ductile polymers with a comparably low glass transition temperature were tableted at temperatures ranging from 22-70°C. Lactose served as a brittle reference with a high melting point. The energy analysis included the net and recovery work during compression, from which the plasticity factor was calculated. The respective results were compared to the changes in compressibility obtained via Heckel analysis. Elevated temperatures reduced the necessary work for plastic deformation for the ductile polymers, which was reflected in decreasing values for the net work of compaction and the plasticity factor. The recovery work slightly increased for the maximum tableting temperature. Lactose showed no response to temperature variations. Changes in the net work of compaction showed a linear correlation to the changes in yield pressure, which could be correlated to the glass transition temperature of a material. It is therefore possible to detect material alterations directly from the compression data, if the glass transition temperature of a material is sufficiently low.

Effect of roll compaction pressure on the properties of high drug-loaded piracetam granules and tablets

OBJECTIVE

The aim of this study was to use an alternative granulation technique, solventless roll compaction, and to investigate the effect of the roll compaction pressure on the properties of granules and high-drug-loaded (80%, w/w) immediate release piracetam tablets.Significance. Piracetam commonly manufactured as high drug-loaded tablets by wet granulation with an aqueous binder solution. Due to its high solubility in water, the wet granulation process is largely susceptible to processing methods and can induce the uncontrolled polymorphic transition of piracetam as well as convert it into mono- and di-hydrates.

METHODS

The blends, comprising of piracetam, Kollidon® 30, and Avicel^® PH-101 were roll compacted at 4, 5 and 13 MPa hydraulic pressure and calibrated using an industrial roll compactor. The resultant granules milled and raw piracetam were investigated with DSC. The resultant granules mixed with Ac-Di-Sol^®, Aerosil^® 200 Pharma, and magnesium stearate to prepare tablets using an industrial tablet press at the same compression force and 25, 65, and 100 rpm. The obtained tablets were film coated with an aqueous dispersion of Opadry^® II using a pilot-scale solid-wall pan coater.

RESULTS

Roll compaction pressure influenced the polymorphic composition of piracetam, the granule properties and tablet mixture in relation to morphology, particle size, flowability, bulk and tapped density, as well as tablet hardness, tablet friability, disintegration, and dissolution.

CONCLUSION

This study showed the roll compaction can be successfully used for the preparation of highly water-soluble, highly drug-loaded piracetam film-coated tablets avoiding wet granulation pitfalls.

Moisture Transport Coefficients Determination on a Model Pharmaceutical Tablet

In this work, a novel methodology to determine moisture transport coefficients for MMC PH101 tablets is presented. Absolute permeability, moisture diffusion, moisture transfer, and water vapor permeability coefficients were estimated on compressed powder tablets produced with different compression pressures (20 MPa to 200 MPa with an interval of 20 MPa). The ASTM D6539 standard test was used to measure the absolute permeability. The moisture transfer coefficient was determined from measured absolute permeability. The moisture diffusion coefficient was obtained with the tablet average pore radius, which was determined with the water droplet penetration method. Descriptive and phenomenological models derived from the measurements were confronted with existing and adopted models, and a good agreement was found. The obtained models are of the function of the microstructural properties of the tablet (average pore radius and average porosity). The tablet average porosity was found to be the principal parameter that governs the behavior of the moisture transport coefficients. The findings of this study might be applicable to obtain a series of input parameters for modelling software, such as COMSOL Multiphysics®, to infer delamination, sticking, and failure propensity from the effect of moisture.

An experimental investigation of temperature rise during compaction of pharmaceutical powders

During pharmaceutical powder compaction, temperature rise in the compressed powder can affect physiochemical properties of the powder, such as thermal degradation and change in crystallinity. Thus, it is of practical importance to understand the effect of process conditions and material properties on the thermal response of pharmaceutical formulations during compaction. The aim of this study was to examine the temperature rise of pharmaceutical powders during tableting, in particular, to explore how the temperature rise depends on material properties, compression speed and tablet shape. Three grades of microcrystalline cellulose (MCC) were considered: MCC Avicel pH 101, MCC Avicel pH 102 and MCC DG. These powders were compressed using a compaction simulator at various compaction speeds (10-500mm/s). Flat faced, shallow convex and normal convex tablets were produced and temperature distributions on the surface of theses tablets upon ejection were examined using an infrared thermoviewer. It was found that an increase in the compaction speed led to an increase in the average surface temperature. A higher surface temperature was induced when the powder was compressed into a tablet with larger surface curvature. This was primarily due to the increasing degree of powder deformation (i.e. the volume reduction) and the effect of interparticule/wall friction.

Use of Compaction Energetics for Understanding Particle Deformation Mechanism

A primary goal of the current work was to examine the potential use of compaction energetics as a tool to predict particle deformation mechanism. Three deformation models, namely, those developed by Heckel, Walker, and Gurnham, were first used to evaluate the deformation mechanisms of 11 commonly used excipients. To complement the information gained from the deformation models, the mechanical energy used in tablet formation was then examined. It has been found that the sum of the work in the compression and decompression phases (plastic work) is a relatively good indicator of a material's plasticity. Conclusions based on this indicator regarding deformation mechanism for the different diluents used were in good agreement with those obtained from the different deformation models studied.

Thermodynamic analysis of compact formation; compaction, unloading, and ejection. I. Design and development of a compaction calorimeter and mechanical and thermal energy determinations of powder compaction

The aim of this investigation was to determine and evaluate the thermodynamic properties, i.e. heat, work, and internal energy change, of the compaction process by developing a 'Compaction Calorimeter'. Compaction of common excipients and acetaminophen was performed by a double-ended, constant-strain tableting waveform utilizing an instrumented 'Compaction Simulator.' A constant-strain waveform provides a specific quantity of applied compaction work. A calorimeter, built around the dies, used a metal oxide thermistor to measure the temperature of the system. A resolution of 0.0001 degrees C with a sampling time of 5 s was used to monitor the temperature. An aluminum die within a plastic insulating die, in conjunction with fiberglass punches, comprised the calorimeter. Mechanical (work) and thermal (heat) calibrations of the elastic punch deformation were performed. An energy correction method was outlined to account for system heat effects and mechanical work of the punches. Compaction simulator transducers measured upper and lower punch forces and displacements. Measurements of the effective heat capacity of the samples were performed utilizing an electrical resistance heater. Specific heat capacities of the samples were determined by differential scanning calorimetry. The calibration techniques were utilized to determine heat, work, and the change in internal energies of powder compaction. Future publications will address the thermodynamic evaluation of the tablet sub-processes of unloading and ejection.